Milorganite is a fertilizer made in Milwaukee, Wisc., from treated sewage sludge. It is categorized as a natural fertilizer because 85 percent of its ingredients are organic, although the U.S. Department of Agriculture does not allow its use in certified organic agricultural production. It is not compost. Unlike chemical fertilizers, it releases nutrients slowly, so it may be a better choice for preventing excess nutrients draining into waterways and groundwater.

Manufacturing Process

The sewage-treatment process adds microbes and oxygen to wastewater collected from the Milwaukee area. After the microbes consume the nutrients in the sludge, a clumping agent is added. The material is pressed and then dried with high heat, which kills pathogens. This results in a dried, pelleted fertilizer.

Composition

Fertilizer composition is listed in ratios of NPK -- nitrogen, phosphorus and potassium. Milorganite contains 5 percent nitrogen, 2 percent phosphorus and .32 percent potassium. It also contains the secondary nutrients calcium, 2.1 percent, sulfur, .58 percent and magnesium, .68 percent, as well as 4 percent iron. It has traces of other micronutrients, such as zinc, copper, boron and chloride.

How It Works

Milorganite is made up of 85 percent organic material. Organic materials release nutrients to plants over time, so are known as slow-release fertilizers. While overapplication of chemical fertilizers can burn plants, organic ingredients won’t. Instead of a quick, chemical boost, microbes in the soil digest the nutrients in Milorganite and deliver them to plants over a period of two to three months. The nutrients stay in the soil until conditions are optimum for plants to take them up during the growing season.

Usage

Many parks, sports fields and golf courses rely on Milorganite to fertilize large, grassy areas. It can be applied anytime during the growing season because it doesn’t contain anything that will burn grass. High temperatures, drought and rainfall do not prevent Milorganite application. It does not need to be watered in, although during the dry season, watering will push the material into the soil faster.

Safety

Milorganite is approved for home gardening use by the Environmental Protection Agency. Miloganite is not toxic to humans or pets. Because its source is wastewater, however, it may contain traces of pharmaceuticals. Because of Milorganite’s relatively high iron content, it is likely to cause stomach upset and vomiting if a handful or more is eaten. Store all fertilizers away from children and pets.

About the Author

Since 1981 Janet Bayers has written on travel, real estate trends and gardening for "The Oregonian" newspaper in Portland. Her work also has appeared in “Better Homes & Gardens,” “Traditional Home,” “Outdoor Living” and other shelter magazines. She holds a Master of Arts in linguistics from Michigan State University.